I'm just curious to know if anyone has had batteries last longer than 3 months for their wireless mouse? When we purchased our iMac this past February, the Apple rep told me her mouse battery had lasted since last summer (7-8 months) and that she used it all the time. Ours have lasted 2 months and 2 1/2 months, respectively, since our purchase. I see now that our keyboard batteries are also low (5 months since purchase). I'm just wondering if this is the norm?

Depends on the battery type and the usage.
I use rechargeables (Eneloop from Costco) and they last, maybe, three weeks. But it's trivial to replace them and put the depleted ones in the charger.
Alkaline batteries might not last much longer than rechargeables, so that's a lot of batteries in a year.
Lithium batteries will last much longer, but they can't last forever.

The Magic Mouse goes to sleep when left alone, so if you use it little, its batteries will last a long time. Every time you move it or click it, you wake it up.

My wireless keyboard and Magic Trackpad batteries last longer than the mouse batteries.

"Design is not just what it looks like and feels like. Design is how it works."
Steve Jobs

I used to get maybe 2-3 weeks out of a set of batteries on my Magic Mouse. Then Apple sent out an update that was supposed to deal with battery life and it did. Now I get at least three months of life out of a set of batteries.

And I would add that I never flip the mouse over and turn it off like I should overnight. So it's always on and using current even when in the sleep mode. If I would think of it I could turn it OFF with the switch each night and get even more battery life.

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Always burn your bridges. You never know who's coming up from behind.

What a good idea, Richard, to turn the mouse off at night. We have never done that but will include it in our evening routine to put our iMac to sleep. I will also try not to play with the mouse while I am reading online. Thanks for your response. We are very appreciative of this forum and the thoughtfulness and sharing of expertise expressed in answering questions.

Another factor to consider, maybe, is whether your Mac stays asleep at night. Theoretically, you should be able to walk away and the Mac will sleep on cue (set in Energy Saver prefs), then, presumably, the mouse and keyboard would consume the least possible current. There are many processes that can prevent a Mac from sleeping, and others that can wake it from sleep.

So it might be worth checking to see that in the morning, your Mac is really asleep. If it isn't, or isn't always, you could track down what's keeping it up or waking it.

"Design is not just what it looks like and feels like. Design is how it works."
Steve Jobs

I too get about 3 months of battery life from my Magic Mouse. Annoying but not disastrous. You may recall a flurry of web postings around the time of the last Snow Leopard upgrade (10.6.7 ?) where numerous people were reporting that the Mouse control panel no longer displayed a correct "percent remaining." I too experienced this with the control panel always reporting "100%." So far as I know, that little issue has never been resolved.